A tight turning radius is very important for riding lawnmowers to mow grass around objects such as trees. Zero turn mowers are very good for mowing around objects since their turning radius is very small. However, the cost of a zero turn mower is very high compared to typical riding lawnmowers, and the driving of a zero turn mower using two levers is perceived to be difficult for many consumers. Further, the hydrostatic transmissions are very inefficient. Most zero turn mowers have the engine in the rear of the mower and caster wheels in the front. An example of a zero-radius turn mower is disclosed in Schaedler, et al., U.S. Pat. No. 7,992,659, which is incorporated herein by specific reference for all purposes.
A standard riding mower with the engine in the front that uses a steering wheel to turn the front wheel has a limited turning radius. Further, the tightest turning radius is only achievable at a moderate speeds and on ideal surfaces. Under most conditions, the mower tries to push forward and slide the front tires rather than turn in accordance with the actual turning direction of the front tires. Attempts have been made to use a zero turn type transmission with caster wheels on a standard mower; however, on side hills or slopes the front end of the mower tends to drift downhill due to the weight of the engine in the front of the mower, thereby making it difficult to drive in a straight line forward.
To achieve the best cutting performance, most manufacturers recommend cutting grass with the engine at its maximum RPM. This requires a transmission that can vary the ground speed of the mower while the engine RPM is constant. Most prefer a ground speed range of 1 to 6 miles per hour and the mower must be capable of a reverse motion and speed control as well.
The typical riding mower has a steering wheel that is mechanically connected to steering rods or linkages that turn the front wheels and has a foot pedal that controls the ground speed and direction via a hydrostatic type transmission. However, some mowers use a geared transmission that requires the user to shift gears for speed and direction.